Temperature-triggered on-demand drug release enabled by hydrogen-bonded multilayers of block copolymer micelles

We report on hydrogen-bonded layer-by-layer (LbL) films as a robust, reusable platform for temperature-triggered "on-demand" release of drugs. Films with high drug loading capacity, temperature-controlled on-off drug release, and stability at physiological conditions were enabled by assembly of tannic acid (TA) with temperature-responsive block copolymer micelles (BCMs), which were pre-formed by heating solutions of a neutral diblock copolymer, poly(N-vinylpyrrolidone)-b-poly(N-isopropylacrylamide) (PVPON-b-PNIPAM), to a temperature above the lower critical solution temperature (LCST) of PNIPAM. The BCM/TA films exhibited temperature-triggered swelling/deswelling transitions at physiological conditions (swelling ratios of 1.75 and 1.2 at 37 degrees C and 20 degrees C, respectively). A model drug, doxorubicin (DOX) was incorporated into the film at a high drug-to-matrix ratio (similar to 9.3 wt.% of DOX per film mass), with a total loading capacity controlled by the film thickness. At 37 degrees C, DOX was efficiently retained within the hydrophobic BCM cores of BCM/TA films, whereas exposure to a lower temperature (20 degrees C) triggered fast DOX release. While neither bare BCM-containing films nor films loaded with DOX showed cytotoxicity at 37 degrees C, drug released from films at lower temperature exhibited high potency against breast cancer cells. Repeated on/off drug release was demonstrated with 1.5-mu m-thick DOX-loaded films, allowing at least three 30-min cooling cycles with consistent DOX (similar to 12-16% of loaded DOX released for each cycle) released over a 4-day period. Despite significant stress associated with multiple swelling/deswelling cycles, films maintained their structural integrity in PBS, and each film could be repeatedly loaded with drug and used more than 15 times with only similar to 7% loss in film thickness and no obvious changes in reloading capacity or release profiles. This work presents the first proof-of-concept utility of temperature-responsive BCM-containing films for repeated on-demand release of a drug. (C) 2013 Elsevier B.V. All rights reserved.